transistor and 5v mirco switch circuit

Hi, I am looking for help to solve the problem in using Arduino UNO to control 24V DC by using 5v micro switch control by transistor given by signal from UNO.

The 5V voltage was directly extract from UNO and connect to 5V mirco switch, in between a transistor. When transistor on, ( signal HIGH from UNO), the voltage in between path given 4.6 volt only. And it was given 5 volt while UNO given LOW and transistor off.

i realize some internal resistance induced from.transistor and get your advise solve this problem simply, say in conjunction with addition 3.3 volt from UNO to 5 volt path.. But how can i up to avoid.short circuit or back emf?

The circuit.setup is mainly refernce to arduino reference book. transistor: 2n3904 microswitch:massuse ME -4L1-5B

Many thanks to yours valuable idea and support

Best regards, Frank


Your best chance here is to post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Then we can comment on your setup.

Do you have a resistor between the transistor base and the 5V from the Arduino? If so what value is the resistor?

Thanks.. Tom.. :)

Hi Tom, Attached was about the circuit diagram, and please comment on it.

Regards, Frank

Seems loss attachmen and
. resend message.



You circuit uses a MOSFET not a BJT transistor you are using.

You need to use this circuit, R1 can be 1K.

You may have already damaged the transistor by connecting the 5V output directly to the base.

Tom... :slight_smile:

Hi Tom,

let me check my part. and thanks for your comment. And i guess the mentioned circuit will have few %voltage drop along the connection from 5V to ground.. or not. If yes, it should not sufficient voltage enough to turn off the 5V micro switch.....So, should we provide compensate the voltage over than 5v?

Regards, Frank

“Microswitch”: Miniature snap-action switch - Wikipedia

“relay”: Relay - Wikipedia

Hi Mark, thanks, but this is basic relay principle, but seems not be the valuable to tackle the problem.

Hi bros, is there anyone happened similar problem in your project due to usage of transistor and how to.overcome using arduino UNO? i check the switch nominal voltage range from 5V to 10V in coil size.

the about the model and spec of switch.

And seek yours

07-08-5305.pdf (115 KB)

If you call a relay a switch you simply confuse people! A switch is a switch, a relay is a relay, that's universal usage in English. Changing the subject line to say "relay" and not "mirco switch" will help people in the future who search these forums.

The answer to your question is the circuit in #4 I think, although I have some difficulty being sure what you are asking. Is the relay coil rated 5V or 24V - or is 24V just the load? Where was this 4.6V you measured in the circuit?

surely cant confuse you, as expert like you.
it should be relay.

attached show my measurement point in my circuit, and is there any idea to tackle the problem?



Have you changed your circuit as I showed you so you can use your transistor?
Can you measure these voltages please.

GND to Collector, with Arduino Output LOW then HIGH
GND to Base, with Arduino Output LOW then HIGH.

Please make sure R1 is in circuit.

Thanks .. Tom.. :slight_smile: